1. Field of the Invention
The present invention relates to portable communication devices such as pagers and cellular telephones and more particularly to the use of a piezoelectric device which operates primarily as a battery charger for the communication device, but which can also be switched to act as a silent or vibration alarm to alert the user of an incoming call or page.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
The use of pagers and cellular telephones has increased at an almost explosive rate over the last decade. At the same time, the using public continues to demand that the pagers and cellular telephones be smaller and less obtrusive while at the same time have a longer and longer service time before the batteries are exhausted. The miniaturization of such devices has been largely successful. However, one of the physically largest and heaviest components has always been and continues to be the battery that powers the device. Thus, it is seen that the demands for both miniaturization and longer service time are in conflict and present an engineering challenge.
In the past, these conflicting demands had been partially solved by significantly increasing the efficiency of the battery to allow for longer use with smaller batteries. In addition, miniaturization of the communication device circuitry components has also helped solve the problem. However, circuit components are now very small and unfortunately further miniaturization may help somewhat in power consumption, but the actual weight and size of most of the components are so small that further reduction could be of little benefit. There are a few components, such as for example the housing or case of the device and the keypads used for dialing in a cellular telephone where further size reduction is extremely difficult since if the keys are not spaced sufficiently apart from each other it becomes difficult to select a single key. One component used by both pagers and cellular telephones which uses a significant amount of energy, is expensive, and rather large is the silent or vibration alarm. Typically, a small electrical motor is used to drive or rotate an unbalanced wheel to cause vibration to provide the silent alarm. These motors simply cannot be made much smaller and still drive a large enough vibration device to be useful. Further, in addition to being a relatively expensive component of the communication device, when actually operating they use a significant amount of the available battery power.